It has been a long known practice to embed anchors of various designs in poured concrete structures by mounting the anchor to some portion of the form into which the concrete is poured, usually a wooden framework which serves as a template or mold for the initially fluid concrete. After the concrete has set and hardened, the form is disassembled and removed to expose the concrete as well as the anchors set therein. A hoist line provided wtih a suitable coupler, for which many designs exist, may then be connected to one or more partially embedded anchors and the concrete structure then erected, lifted or otherwise handled in a convenient and safe manner.
One commonly used type of hoist anchor is the so-called "dog bone" anchor consisting of a straight steel shaft terminating at each end in an enlarged anchor head. Most of the shaft as well as one head is embedded in concrete while the opposite head and a short portion of the anchor shaft remain exposed within a hemisperhical depression in the concrete surface. Such anchors are used with hoist coupling devices which include a hemispherical coupler body designed to mate into the hemispherical depression and receive the exposed anchor head. A latching mechanism locks the anchor head within the coupler body preventing separation of the two during hositing of the concrete structure.
The "dog bone" anchor is typically set in the poured concrete structure by first fitting one end of the anchor i.e., the end that is to remain exposed, within a hemipherical rubber void. The rubber void is a solid rubber body of hemispherical shape, i.e. having a flat top surface and a hemispherical undersurface. The hemispherical portion of the body is split diametrically through most of the height of the void body, the height being the radius line perpendicular to the flat top surface, so that the two halves remain joined by a relatively small thickness of rubber at the flat top surface. It is therefore possible to spread apart the two halves of the void body at the split line with a resilient flexible hinged connection joining the two halves. A cavity shaped to receive the anchor head is centered in the void body and this cavity opens to the exterior at the center of the hemispherical undersurface. The cavity is divided equally between the two havles of the void body. One head of the anchor is inserted into the void body cavity and is captured between the two halves. The cavity opening narrows around the anchor shaft and prevents the larger anchor head from being withdrawn unless the void body halves are spread apart. The rubber void is then mounted, by means of screws or the like, to the inner surface of the wooden form so that the rest of the anchor extends into the form cavity into which concrete is to be poured. The flat side of the rubber void is fixed to the form surface, which keeps the ruvbber void from spreading open and holds the anchor in place until the concrete is poured and sets. After the wooden form is removed, the rubber void is cut away and discarded, leaving a hemisperhical void in the concrete with the exposed anchor head fixed therein in proper position for mating with an appropriate hoist coupler.
Difficulties have been experienced in the past with this approach due to the susceptibility of fluid concrete to leak into the rubber void and enter the anchor head cacity where the concrete solidifies, making subsequent removal of the rubber void difficult and making it impossible to connect the hoist coupler to the anchor head until the solidified concrete has been removed. These difficulties introduce delays and increase the cost of a construction project. A continuing need exists therefore for improved methods and equipment for setting the anchor hoists in poured concrete structures which will positively exclude concrete from the rubber voids to eliminate the aforedescribed problem.